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Anaerobic Digestion of Biomass
Jiqin Ni (jee-chin nee), Ph.D.Dept. of Agricultural and Biological Engineering
Purdue University, West Lafayette, Indiana
WIndiana
Indiana Convention Center, Indianapolis
July 20, 2011
What is Anaerobic Digestion
• A microbiological process
that anaerobically (in the
absence of oxygen)
decomposes
biodegradable materials.
• Consisting three main
phases (hydrolysis,
acidogenesis, and
methanogenesis).
Source: Aarhus Uni. Denmark
What is Biogas
• A combustible mixture of gases
• Other names: manure gas, methane gas, marsh
gas, etc.
Compound %
Methane (CH4) 50–75
Carbon dioxide (CO2) 25–50
Hydrogen sulfide (H2S) 0–3
Hydrogen (H2) 0–1
Nitrogen (N2) Trace
Ammonia (NH3) Trace
Oxygen (O2) Trace
Source: Aarhus Uni. Denmark
A Brief History
• 1859: the first sewage plant in Bombay,
Indian;
• 1895: a digester in U.K. lighted street lamps;
• 1970s-1980s: wide application in the world
• 2000s - : application steadily increasing
Photo: HEEE, China
Biomass for Anaerobic Digestion
Animal Wastes
Agro-industrial (food processing) wastes
Municipal wastes
Estimation of Biogas Production
• Based on COD
1 kg COD = ~ 0.35 m3 methane
• Based on total solid (TS)
Manure TS, %Biogas production
CH4, %m3/t manure m3/t TS
Cow 18~20 40~50 210~300 60
Hog 20~25 55~65 270~450 60
Poultry 30~32 70~90 250~450 60
Biogas Resources
• Sufficient quantity
• Long term stability
• High concentration
• Animal wastes
• Agro-industrial wastes
• Municipal wastes
• Crop residues
• 2134 CFO and CAFO in 2010
• Manure production:
9.1 million tons/yr
• Potential biogas production:
455 M m3/yr (16.1 B ft3/yr)
Equivalent to 9.7 B ft3/yr natural gas,
about 2% of total Indiana natural
gas consumption
Source: www.Indianamap.org
Animal Wastes in Indiana
Environmental Benefits
• Reduce greenhouse gas effects
• Reduce odor.
• Reduce BOD and TSS by 80-90%.
• Reduce pathogen.
• Effective in killing weed seeds.
• Retain most of the nutrient content in digested manure.
• Mineralize organic nitrogen (Org-N) to ammonia (NH3-N).
Fermentation Process
Temperature
• Thermophilic: 50-55 ℃, up to 70 ℃
• Mesophilic: optimally around 30-38 ℃, or 20-45 ℃
• Fermentation rate doubles at T increase of 10 ℃
Solid content
• Normally 5-12% total solid (TS)
Hydraulic retention time (HRT) for animal wastes
• Thermophilic:10-15 days
• Mesophilic: 20-25 days
Digester Design: Plug flow
Plug TransportSource: Ben Teague
PROS
•Low maintenance
•Batch or semi-batch operation
•Rapid recovery/low retention time
•Can be used in different climates
CONS
•Comparatively expensive
•Smaller reactor volume
•Labor intensive
A plug-flow digester in Germany(Photo: Dr. K. Sheng)
Digester Design: Covered Lagoon
PROS
•Least expensive
•Low maintenance
•Low solids manure
CONS
•Land availability
•Efficient only in high temp climates
•High retention time
Source: Ben Teague, Mississippi Technology Alliance, Mississippi Alternative Energy Enterprise
Other Digester Types
1. Batch- fed reactor
2. Suspended particle
3. Anaerobic filter
4. Up-flow solids reactor
5. Up-flow sludge blanket reactor
6. Anaerobic pump digester
7. Fluidized - and expanded - bed
8. Fixed film
Basic module 800,000 gallons
TIREPower Anaerobic Digester
1/20th Scale 2005/2006
Source: TIREPower LLC
Users Biogas
Dairy
100-head
Milk plantBiogas
tank
80 m3
Biogas
200 m3
at 25 C
Anaerobic
digester
Manure
60 C water
Biogas for Cooking, Heating, & Lighting
Layer Farm Digester System in China
8000 m3
UASB
digester
1000 m3 biogas holder
Boiler Generator Restaurant
1500 m3 x 4
SBR
Photos: Hangzhou Energy & Environmental Engineering Co. Ltd.
Biogas for Electricity Generation
Animal Biogas production, ft3/d kWh/hd/day
Cow 65-80 2.5-3.7
Beef feeder 45-55 1.8-2.2
Sow 5.0-7.5 0.2-0.3
Finisher 3.5-5.5 0.15-0.22
Nursery 1.4-2.1 0.06-0.09
Laying hen 0.25 0.01
Biogas generators in Germany(Photos: Dr. K. Sheng)
Biogas Use in Vehicles
A biogas bus in Linköping, Sweden (www.Wikipedia.com)
Biogas station and
biogas car in Germany(Photos: Dr. K. Sheng)
Biogas Processing for Vehicles
PurificationCH4: from 60% to 95%CO2: from 35% to 3%H2S: < 10 ppmO2: < 0.5%
CompressionInto cylinder: 250 atm
Storage/transportation
1 m3 (35 ft3) bio-fuel = 1.2 L (0.3 gal) gasoline
Source: HEEE, China
A Future Trend of Biogas Use
A 20,000m3/d vehicle bio-fuel
biogas system under
construction in China
Indiana’s Fair Oaks Farms later this year: 42 new trucks - powered by
biogas from 6 digesters -- to deliver milk in Indiana, Kentucky and
Tennessee.
Source: HEEE, China
Biogas in Germany
• Biogas electricity generation system: from 450 in
1997 to 4,500 in 2007
• Capacity: from 100 MW in 2000 to 1,700 MW in 2007
• Increased bio-fuel for vehicles and natural gas grid
• World’s larges biogas system using corn stalks
(250,000 m3/d) built in 2009
Source: HEEE, China
Biogas in Switzerland
• The first country using biogas in vehicles
• 15,000 buses and taxies in Bern using bio-fuel.
• Biogas resources: municipal wastewater sludge and
biological wastes
Biogas in China
• Large and medium size digester systems: 2,761 in 2008
• Millions of small family-size digesters
• Biogas production: equivalent of 0.34% of national natural
gas consumption
• Biogas use: heat and electricity generation, started vehicle
fuel use
Photos: HEEE, China
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